The early-type eclipsing binary V1331 Aql★

We present a spectroscopic and photometric analysis of V1331 Aql, an early-type eclipsing binary with a quite short period, i.e. 1.364 d. Radial velocity curves of both components were constructed from high-dispersion spectra of this close early B-type system, which are the first published spectroscopic measurements of this star. The light curve analysis is based on new UBV curves. Absolute dimensions of the binary components are derived. The primary mass M1 (=10.1 M⊙) and radius are close to the expected ZAMS values for type B1 V. The mass of the secondary component M2 (=5.3 M⊙) corresponds to B4 IV, but the component is hotter than expected for this type. It is oversized and overluminous for such a mass, and in this respect is similar to the secondary components of semi-detached Algol-like systems. However, it does not completely fill its Roche lobe. A revision of the few other known binaries of comparable spectral type and period and a recalculation of the parameters of AI Cru and V Pup suggests that the detached configuration of V1331 Aql is unique among this group.